A Mach-Zehnder interferometer (MZI) structure is presented and fabric ated by offset-splicing a single mode fiber, multi-core fiber,multi-mode fiber and single mode fiber.The proposed MZI senso r can be used for simultaneous measurement of temperature and refractive index.The measuremental principle of MZI sensor is analyzed theoretically.The experiment results show that the peak wavelength of transmission spectrum of the sensor shi fts linearly with the change of temperature, and the temperature sensitivity is 54.238pm/℃.The peak intensity of t ransmission spectrum of the sensor is not sensitive to the temperature change,but shifts linearly with the c hange of refractive index,and the refractive index sensitivity is 10.704dB/RIU.The pe ak wavelength of transmission spectrum of the sensor is not sensitive to the refractive index change.So the te mperature and refractive index can be measured synchronously by monitoring the change of the peak wavelength or intens ity of the interference fringe.Due to the wavelength modulation and intensity modulation methods used for temperatu re and refractive index measurement, respectively,the sensor can overcome the cross-sensitive problem of two-parame ter measurement simultaneously.The sensor has many inherent advantages,including simple structure,easy fabrication,h igh sensitivity and so on,Which ensures its wide applications in the fields of b iology,chemistry and medicine.